Solid state image sensors, also known as imagers, have commonly been used in various photo-imaging applications. An imager absorbs incident radiation of a particular wavelength (such as optical photons or x-rays) and generates an electrical signal corresponding to the absorbed radiation. There are a number of different types of semiconductor-based imagers, including charge coupled devices (CCDs), photodiode arrays, charge injection devices (CIDs), hybrid focal plan arrays, and complementary metal oxide semiconductor (CMOS) imagers. These imagers, when used with appropriate imaging circuits, capture, process and display images for various purposes. Current applications of solid state imagers include cameras, scanners, machine vision systems, vehicle navigation systems, video telephones, computer input devices, surveillance systems, auto focus systems, star trackers, motion detector systems, and image stabilization systems among other uses.
Imagers are typically formed with an array of pixel cells containing photosensors, where each pixel cell produces a signal corresponding to the intensity of light impinging on that element when an image is focused on the array. The signals may then be stored, for example, to display a corresponding image on a monitor or otherwise used to provide information about the optical image. Photosensors are typically photogates, phototransistors, photoconductors or photodiodes. The magnitude of the signal produced by each pixel cell is proportional to the amount of light impinging on the photosensor.
To capture a color image, a color filter array (CFA) is typically employed and placed in front of the array of pixel cells. For example, each pixel cell is covered with a color filter, such as e.g., a red (R), green (G) or blue (B) filter. In a typical CFA layout, the red, green, and blue filters are arranged in a mosaic sequential pattern, such as a Bayer filter pattern, which is quartet-ordered with successive rows that alternate red and green filters, then green and blue filters. When a CFA is used, photosensors separately detect red, green or blue photons.
When using the CFA technique to differentiate colors, the quantum efficiency of an imager can be compromised as color filters allow only a narrow spectral band of incident light (e.g., red, green, or blue light) to pass through while absorbing the rest of the photo energy. Color filter arrays made by current CFA manufacturing processes can also be susceptible to a number of process issues, such as non-planarity and streaks, which can lead to fixed pattern noise and other defects. Moreover, a captured image having individual color pixels must then be processed using a color demosaicing technique, which can increase processing time and the complexity of the imager.
Accordingly, it is advantageous to provide an imager pixel array capable of more efficiently and effectively separating and detecting spectral components of incident light to improve the quantum efficiency of imagers.